Button cell

ABSTRACT

A rechargeable battery includes: a case accommodating an electrode assembly and having an opening; a cap assembly including a cap plate coupled to the case to cover the opening, and a terminal plate coupled to the cap plate; and a direction determining member covering the cap plate and coupled to the case to define an extended part.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean PatentApplication No. 10-2020-0044714, filed on Apr. 13, 2020 in the KoreanIntellectual Property Office, the entire content of which isincorporated herein by reference.

BACKGROUND 1. Field

Aspects of embodiments of the present invention relate to a rechargeablebattery.

2. Description of the Related Art

Unlike a primary battery that is incapable of being recharged, arechargeable battery can be repeatedly charged and discharged. Alow-capacity rechargeable battery may be used for small electronicdevices, such as a mobile phone, a laptop computer, and a camcorder, anda large-capacity battery has been widely used as a power source fordriving a motor of a hybrid vehicle, for example.

A representative rechargeable battery includes a nickel-cadmium (Ni—Cd)battery, a nickel-hydrogen (Ni-MH) battery, a lithium (Li) battery, anda lithium ion (Li-ion) rechargeable battery. Particularly, the lithiumion secondary battery has a higher operation voltage by about threetimes than the nickel-cadmium battery or the nickel-hydrogen batterythat may be used as a portable electric equipment power source. Also,the lithium ion secondary battery may be widely used in that energydensity per unit weight is high.

In particular, as a demand for wearable devices, such as headphones,earphones, smart watches, and body-mounted medical devices which useBluetooth, has increased, the demand for a rechargeable battery of whichenergy density is high and is ultra-small is increasing.

The ultra-small rechargeable battery has important tasks of providingrequired electrical capacity within a limited size, implementing anefficient structure while improving an effective low weight, andimproving structural stability.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention, and,therefore, it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

SUMMARY

According to an aspect of embodiments of the present invention, anultra-small rechargeable battery is provided. According to anotheraspect of embodiments of the present invention, a rechargeable batteryconfigured to prevent or substantially prevent reverse directioninsertion is provided.

According to another aspect of embodiments of the present invention, arechargeable battery configured to prevent or substantially prevent anexternal short circuit of parts having different polarities in the capassembly is provided.

A rechargeable battery according to one or more embodiments of thepresent invention includes: a case accommodating an electrode assemblyand having an opening; a cap assembly including a cap plate coupled tothe case to cover the opening, and a terminal plate coupled to the capplate; and a direction determining member covering the cap plate andcoupled to the case to define an extended part.

The electrode assembly may include a first electrode, a secondelectrode, and a separator therebetween, the case may be connected tothe first electrode by a first electrode tab, and the terminal plate maybe connected to the second electrode by a second electrode tab.

The cap plate may be electrically connected to the case, and the capplate and the terminal plate may be thermally fused with a thermalfusion member therebetween and are electrically insulated from eachother.

The terminal plate may include: a flange part between the cap plate andthe electrode assembly and electrically insulated from and attached toan inner surface of the cap plate; and a protruded terminal protrudedoutside from the flange part to be inserted into a terminal hole of thecap plate and electrically connected to the second electrode tab via aninner surface of the terminal plate.

An outer surface of the protruded terminal and an outer surface of thecap plate may respectively define a plane surface separated from eachother at a same height based on a bottom of the case.

The direction determining member may include: a plane portion includinga through hole corresponding to the protruded terminal so as to coverthe outer surface of the cap plate while exposing the protrudedterminal; and a side portion extending along a side of the case on anouter surface of the plane portion so as to cover and be coupled to apart of the side of the case.

The direction determining member may include an electrically insulatingmaterial to electrically insulate between the outer surface of theprotruded terminal and the outer surface of the cap plate.

The through hole of the direction determining member may be concentricwith the terminal hole of the cap plate, and the diameter of the throughhole may be smaller than the diameter of the terminal hole to therebycover an entire outer surface of the cap plate at a side of theprotruded terminal.

The direction determining member may include polypropylene (PP),polyethylene (PE), polyethylene terephthalate (PET), polyethylenenaphthalate (PEN) resin, or rubber.

A diameter direction length D1 of the plane portion may be equal to orgreater than a length H1 in a height direction of the side portion(D1≥H1).

The terminal plate may include: a flange part outside the cap plate andelectrically insulated from and attached to the outer surface of the capplate; and a tab connection portion protruded inside from the flangepart to be inserted into the terminal hole of the cap plate andelectrically connected to the second electrode tab via an inner surfaceof the terminal plate.

Based on the bottom of the case, the outer surface of the cap plate maybe covered by the flange part, and a remaining exposed surface isdefined as a plane surface.

The direction determining member may include: a plane portion includinga through hole corresponding to the flange part so as to cover theexposed surface of the cap plate while exposing the flange part; and aside portion extending along a side of the case outside the planeportion so as to cover and be coupled to a part of the side of the case.

Based on the bottom of the case, a height of the plane portion may beequal to or less than a height of the flange part.

A diameter direction length D2 of the plane portion may be equal to orless than a length H2 in the height direction of the side portion(D2≤H2).

The rechargeable battery according to one or more embodiments of thepresent invention may further include an insulating member on anexterior circumference of the tab connection portion and installed tothe inner surface of the cap plate.

The direction determining member may define a step on the side of thecase by the extended part.

The case may define a first diameter in an outer surface in a diameterdirection at the lower portion, and the direction determining member maybe coupled to the upper portion of the case to define a second diameterthat is larger than the first diameter in the diameter direction.

In the rechargeable battery according to one or more embodiments of thepresent invention, since the direction determining member covers the capplate and is coupled to the case, the extended part may be formed. Theextended part forms the step at the side of the case. That is, since thedirection determining member is more protruded than the side of the caseat the cap plate and its adjacent side, the step may be formed with theextended part that has an increased height or diameter. Therefore,visually or structurally, a reverse direction insertion of therechargeable battery may be effectively prevented.

In the rechargeable battery according to one or more embodiments, twoparts of the cap assembly having different polarities (e.g., the capplate and the terminal plate) are exposed in the same direction, and thedirection determining member may cover at least one of two parts havingdifferent polarities. When the direction determining member is formed ofan electrically insulating material, a short circuit of two parts by aconductive foreign material may be effectively prevented.

In the rechargeable battery of one or more embodiments, the extendedpart is formed of the direction determining member coupled to the case,and the extended part may buffer against physical impact, therebyimproving safety, such as in a drop test and a tumbling test.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a rechargeable battery according toan embodiment of the present invention.

FIG. 2 is an exploded perspective view of the rechargeable battery ofFIG. 1 .

FIG. 3 is a cross-sectional view taken along the line III-III of FIG. 1.

FIG. 4 is a perspective view showing a rechargeable battery according toanother embodiment of the present invention.

FIG. 5 is an exploded perspective view of the rechargeable battery ofFIG. 4 .

FIG. 6 is a cross-sectional view taken along the line VI-VI of FIG. 4 .

DESCRIPTION OF REFERENCE DESIGNATORS

1, 2: rechargeable battery 10: electrode assembly 11: first electrode12: second electrode 13: separator 14: insulating sheet 20: case 21:opening 30, 60: cap assembly 31: cap plate 33, 63: terminal plate 34:thermal fusion member 40, 70: direction determining member 41, 71: planeportion 42, 72: side portion 51: first electrode tab 52: secondelectrode tab 61, 62: insulating member 101: first end 102: second end301: exposed surface 311: terminal hole 331, 631: flange part 332:protruded terminal 341: through hole 411, 711: through hole 611, 621:through hole 632: tab connection portion D: battery diameter D1, D2:diameter direction length D3: first diameter H: height H1, H2: length ofheight direction P1, P3: extended part P2, P4: non-extended part ΔH:height difference

DETAILED DESCRIPTION

The present invention will be described more fully herein with referenceto the accompanying drawings, in which some example embodiments of theinvention are shown. As those skilled in the art would realize, thedescribed embodiments may be modified in various different ways, allwithout departing from the spirit or scope of the present invention. Thedrawings and description are to be regarded as illustrative in natureand not restrictive. Like reference numerals designate like elementsthroughout the specification.

Also, in this specification, it is to be understood that when onecomponent is referred to as being “connected” or “coupled” to anothercomponent, it may be connected or coupled directly to the othercomponent or connected or coupled to another component with one or moreother components intervening therebetween. On the other hand, in thisspecification, it is to be understood that when one component isreferred to as being “connected or coupled directly” to anothercomponent, it may be connected or coupled to the other component withoutanother component intervening therebetween.

It is also to be understood that the terminology used herein is only forthe purpose of describing particular embodiments, and is not intended tobe limiting of the invention.

Singular forms are to include plural forms unless the context clearlyindicates otherwise.

It is to be further understood that terms such as “comprises,”“includes,” or “have” used in the present specification specify thepresence of stated features, numerals, steps, operations, components,parts, or a combination thereof, but do not preclude the presence oraddition of one or more other features, numerals, steps, operations,components, parts, or a combination thereof.

It is to be understood that, although the terms “first,” “second,” etc.may be used herein to describe various elements, these elements shouldnot be limited by these terms. These terms are used to distinguish oneelement from another. For example, a first element could be termed a“second” element, and, similarly, a second element could be termed a“first” element, without departing from the scope of example embodimentsof the inventive concept. The terms of a singular form may includeplural forms unless the context clearly indicates otherwise.

In addition, terms such as “below,” “lower,” “above,” “upper,” and thelike are used to describe the relationship of the configurations shownin the drawings. However, the terms are used as a relative concept andare described with reference to the direction indicated in the drawings.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which the inventive concept pertains. Itis also to be understood that terms defined in commonly useddictionaries should be interpreted as having meanings consistent withthe meanings in the context of the related art, and are expresslydefined herein unless they are interpreted in an ideal or overly formalsense.

A rechargeable battery according to an embodiment of the presentinvention, which is an ultra-compact battery, may be a coin cell or abutton cell. Here, the coin cell or the button cell is a thin coin-typeor button-type cell, and refers to a battery having a ratio (H/D) of aheight (H) to a diameter (D) (see FIG. 1 ) of 1 or less.

In an embodiment, the coin cell or the button cell is cylindrical, and ahorizontal cross-section is circular, but the present invention is notlimited thereto, and a horizontal cross-section may be oval orpolygonal. In this case, a diameter is set to a maximum distance of acase (or a direction determining member) outer circumference based on ahorizontal direction of a battery, and a height is set to a minimumdistance between a case of a battery and an outer plane of a cap plate(or a direction determining member).

However, the present invention is not limited to the coin cell or thebutton cell that are provided as examples of the present invention, anda battery of the present invention may be a cylindrical-type or pin-typebattery. Herein, a case in which a rechargeable battery according to anembodiment of the present invention is a coin cell or a button cell willbe described in further detail.

FIG. 1 is a perspective view showing a rechargeable battery according toa embodiment of the present invention; FIG. 2 is an exploded perspectiveview of the rechargeable battery of FIG. 1 ; and FIG. 3 is across-sectional view taken along the line III-III of FIG. 1 .

Referring to FIG. 1 to FIG. 3 , a rechargeable battery 1 according to anembodiment includes an electrode assembly 10, a case 20, a cap assembly30, and a direction determining member 40. The cap assembly 30 includesa cap plate 31 and a terminal plate 33 coupled to each other. As anexample, the cap plate 31 and the terminal plate 33 are thermally fusedby a thermal fusion member 34 that is disposed therebetween.

In an embodiment, the thermal fusion member 34 acts as a medium tointerconnect the cap plate 31 and the terminal plate 33. For example,the thermal fusion member 34 may be formed of an electrically insulatingmaterial, such as a polymer, and may be melted using a laser or the liketo be fused to the cap plate 31 and the terminal plate 33.

In an embodiment, by coupling the terminal plate 33 to the cap plate 31with the thermal fusion member 34, it is possible to form a stablecoupling structure while effectively insulating between the terminalplate 33 and the cap plate 31 without adding a separate insulatingconfiguration.

Since a coin cell is manufactured in an ultra-compact size, it may havea design limitation in terms of space, and, accordingly, it is desiredto secure functionality while simplifying a structure and amanufacturing process thereof. Regarding this, in an embodiment,insulation and coupling between the terminal plate 33 and the cap plate31 through the heat-fusion member 34 may be realized.

In an embodiment, the electrode assembly 10 includes a first electrode11 (for example, a negative electrode) and a second electrode 12 (forexample, a positive electrode) provided at respective sides of aseparator 13 that is an electrical insulating material, and is formed bywinding the first electrode 11, the separator 13, and the secondelectrode 12. Therefore, the electrode assembly 10 may be formed as ajelly roll type. In another embodiment, although not shown separately,the electrode assembly may be formed as a stack type.

The electrode assembly 10 is configured to charge and discharge acurrent, and a winding axis in the electrode assembly 10 may be arrangedparallel to a height direction (a vertical direction in FIGS. 1 to 3 )of the case 20. In an embodiment, a first end (a lower surface orcross-section of the electrode assembly) 101 and a second end (an uppersurface or cross-section of the electrode assembly) 102 of the electrodeassembly 10 may be flat and parallel to each other. In an embodiment,the electrode assembly 10 is not provided with a center pin, but acenter pin (not shown) may be provided at a position of the windingaxis.

The case 20 accommodates the electrode assembly 10 while facing thefirst end 101 of the electrode assembly 10. In an embodiment, theelectrode assembly 10 is covered with an insulating sheet 14 andaccommodated in the case 20. As an example, the case 20 is formed as acylinder that accommodates the jelly roll type of electrode assembly 10,and the cap assembly 30 seals an opening 21 of the cylindrical case 20.

In an embodiment, the electrode assembly 10 includes a first electrodetab 51 connected to the first electrode 11 and a second electrode tab 52connected to the second electrode 12, and the first and secondelectrodes 11 and 12 are drawn out to the first and second ends 101 and102, respectively.

In a state in which the electrode assembly 10 is accommodated in thecase 20, the first electrode tab 51 is electrically connected to abottom of the case 20, and the second electrode tab 52 is electricallyconnected to the terminal plate 33 of the cap assembly 30.

In addition, the cap plate 31 of the cap assembly 30, while facing thesecond end 102 of the electrode assembly 10, is coupled to the case 20to cover the opening 21. The terminal plate 33 is coupled to the secondelectrode tab 52 while being coupled to the cap plate 31 with thethermal fusion member 34.

Herein, a case in which the first electrode 11 and the second electrode12 are respectively a negative electrode and a positive electrode willbe described as an example, but the present invention is not limitedthereto, and the first electrode 11 and the second electrode 12 mayrespectively be a positive electrode and a negative electrode.

The first electrode 11 is formed in a long extending strip shape, andincludes a negative electrode coated portion that is a region in which anegative electrode active material layer is coated to a currentcollector of a metal foil (for example, a Cu foil) and a negativeelectrode uncoated portion that is a region in which an active materialis not coated. The negative electrode uncoated portion may be disposedat an end portion in a length direction of the negative electrode.

The second electrode 12 is formed in a long extending strip shape, andincludes a positive electrode coated portion that is a region in which apositive electrode active material layer is coated to a currentcollector of a metal foil (for example, an Al foil) and a positiveelectrode uncoated portion that is a region in which an active materialis not coated. The positive electrode uncoated portion may be disposedat an end portion in a length direction of the positive electrode.

The case 20 allows the electrode assembly 10 to be inserted into theopening 21 formed at a side thereof, and has a space for accommodatingthe electrode assembly 10 and an electrolyte therein. In an embodiment,for example, the case 20 is formed in a cylindrical shape having a lowerheight H than a diameter D thereof, and has a circular opening 21 suchthat the cylindrical electrode assembly 10 corresponding to an innerspace thereof may be inserted therein.

In the cap assembly 30, the terminal plate 33 includes a flange part 331and a protruded terminal 332. The flange part 331 is disposed betweenthe cap plate 31 and the electrode assembly 10 to be electricallyinsulated from and attached to an inner surface of the cap plate 31.

The protruded terminal 332 is protruded outside from the flange part 331and inserted into a through hole 341 of the thermal fusion member 34 anda terminal hole 311 of the cap plate 31, and an inner surface of theprotruded terminal 332 is electrically connected to the second electrodetab 52. The second electrode tab 52 may be connected to an inner surfaceof the flange part 331 or the inner surface of the protruded terminal332, or may be connected to both.

In an embodiment, the outer surface of the protruded terminal 332 andthe outer surface of the cap plate 31 form a plane and are spaced apartfrom each other in a diameter direction at a same height based on thebottom of case 20. When assembling the rechargeable battery 1 includingthis structure into a set, in order to prevent or substantially preventa reverse direction insertion, the rechargeable battery 1 according toan embodiment further includes a direction determining member 40.

The direction determining member 40 covers the cap plate 31 and iscoupled to the case 20 to form an extended part P1. That is, thedirection determining member 40 forms a step on a side of the case 20 bythe extended part P1.

Therefore, the direction determining member 40 may define both sides ofthe height direction of the rechargeable battery 1 as an extended partP1 on the upper side and a non-extended part P2 on the lower side. Thatis, in the rechargeable battery 1, the portion to which the directiondetermining member 40 is coupled forms an extended part P1, and theportion without the direction determining member 40 forms a non-extendedpart P2.

In the non-extended part P2, the case 20 and a bottom of therechargeable battery 1 have a negative property of the first electrode11, and in the extended part P1, the terminal plate 33 has a positiveproperty of the second electrode 12. In an embodiment, the cap plate 31coupled to the case 20 has the negative property of the first electrode11 together with the case 20. That is, the cap plate 31 and the case 20are electrically connected to each other.

In an embodiment, for example, the direction determining member 40includes a plane portion 41 and a side portion 42. The plane portion 41includes a through hole 411 corresponding to the protruded terminal 332to cover the outer surface of the cap plate 31 while exposing theprotruded terminal 332. The side portion 42 extends along the side ofthe case 20 from an outer surface of the plane portion 41 so as to becoupled to the side of the case 20 by receiving a part of the side ofthe case 20. In the rechargeable battery 1, the portion to which thedirection determining member 40 is coupled forms the extended part P1,and the portion without the direction determining member 40 forms thenon-extended part P2.

Therefore, the direction determining member 40 forms a step on the sideof the case 20 at a boundary between the extended part P1 and thenon-extended part P2 in the height direction and an intersectingdirection (diameter direction) orthogonal to the height direction. Thatis, the extended part P1 relatively increases the height or diametercompared to the non-extended part P2.

In an embodiment, for the case 20, the direction determining member 40is not coupled at the bottom, such that a first diameter D3 is definedbetween outer sides of the diameter direction of the case 20. Thedirection determining member 40 is coupled to the upper part of case 20and defines a second diameter (same as the diameter D of the battery)between the outside sides of the diameter direction of the directiondetermining member 40. The second diameter D is larger than the firstdiameter D3. Therefore, there is a difference in diameter between theupper portion and the lower portion of the rechargeable battery 1.

In an embodiment, the direction determining member 40 may be formed ofan electrically insulating material to prevent or substantially preventan electrical short circuit between an outer surface of the protrudedterminal 332 and an outer surface of the cap plate 31. For example, thedirection determining member 40 may be formed of polypropylene (PP),polyethylene (PE), polyethylene terephthalate (PET), polyethylenenaphthalate (PEN) resin, or rubber. Although not illustrated, syntheticresins or electrical insulation materials may be applied to thedirection determining member.

In an embodiment, the through hole 411 of the direction determiningmember 40 is concentric with the terminal hole 311 of the cap plate 31,and a diameter of the through hole 411 is smaller than a diameter of theterminal hole 311, such that the direction determining member 40completely covers the outer surface of the cap plate 31 from the side ofthe protruded terminal 332, thereby effectively preventing an externalshort circuit due to a conductive material.

In an embodiment, an insulating member 61 disposed on the outercircumference in the diameter direction of the thermal fusion member 34is installed on the inner surface of the cap plate 31. The insulatingmember 61 may form an electrically insulating structure between the capplate 31 and the second electrode tab 52, and between the cap plate 31and the electrode assembly 10. In an embodiment, the insulating member61 includes a through hole 611 corresponding to the exterior diameter ofthe thermal fusion member 34.

In the direction determining member 40, a diameter direction length D1of the plane portion 41 may be equal to or greater than a length H1 inthe height direction of the side portion 42 (D1≥H1). Therefore, thelength H1 of the height direction forms a clamping force for the case 20of the direction determining member 40, and the diameter directionlength D1 allows the insulation performance of the terminal plate 31 tobe sufficiently secured.

In an embodiment, referring to FIG. 1 , in the rechargeable battery 1,in a state that the opening 21 of the case 20 is closed and sealed bythe cap assembly 30, the height H is defined as a distance between thecase 20 and the outer planes of the direction determining member 40, andthe diameter D of the battery is defined as the exterior circumferenceof the direction determining member 40. In an embodiment, a ratio of theheight H to the battery diameter D is 1 or less (H/D≤1). Therefore, therechargeable battery 1 of an embodiment is a coin-type battery or abutton-type battery and may form a thin coin or button shape.

Herein, another embodiment of the present invention is described.Further description of the same configurations as described above may beomitted, and different configurations are described regarding theembodiment shown in FIGS. 4 to 6 .

FIG. 4 is a perspective view showing a rechargeable battery according toanother embodiment of the present invention; FIG. 5 is an explodedperspective view of the rechargeable battery of FIG. 4 ; and FIG. 6 is across-sectional view taken along the line VI-VI of FIG. 4 .

Referring to FIG. 4 to FIG. 6 , in a rechargeable battery 2 according toanother embodiment, in a cap assembly 60, a terminal plate 63 includes aflange part 631 and a tab connection portion 632. The flange part 631 isdisposed on the outside of the cap plate 31 and is electricallyinsulated from and attached to the outer surface of the cap plate 31.

The tab connection portion 632 is protruded inward from the flange part631 and inserted into the through hole 341 of the thermal fusion member34 and the terminal hole 311 of the cap plate 31, and the secondelectrode tab 52 is electrically connected to an inner surface of thetab connection portion 632.

Based on the bottom of the case 20, a part of the outer surface of thecap plate 31 is covered with the flange part 631, and a remaining partof the outer surface (an exposed surface 301) remaining on the outersurface may be formed as a flat surface. To prevent or substantiallyprevent a reverse direction insertion of the rechargeable battery 2including this structure, the rechargeable battery 2 according to anembodiment includes a direction determining member 70.

For example, the direction determining member 70 includes a planeportion 71 and a side portion 72. The plane portion 71 includes athrough hole 711 corresponding to the flange part 631 so as to cover theexposed surface 301 of the outer surface of the cap plate 31 whileexposing the flange part 631 of the terminal plate 63. The side portion72 extends along the side of the case 20 from an outer surface of theplane portion 71 so as to cover a part of the side of the case 20 and tobe coupled to the side of the case 20. In the rechargeable battery 2, aportion to which the direction determining member 70 is coupled definesan extended part P3, and a portion without the direction determiningmember 70 defines a non-extended part P4.

Therefore, the direction determining member 70 covers the exposedsurface 301 of the cap plate 31 and is coupled to the case 20 to formthe extended part P3. That is, the direction determining member 70 formsa step on the side of the case 20 by the extended part P3. That is, theextended part P3 relatively increases the height or the diametercompared with the non-extended part P4.

Based on the bottom of the case 20, the height of the plane portion 71is the height of the flange part 631 or less. Therefore, the planeportion 71 and the flange part 631 may have a height difference ΔH. Theheight difference ΔH makes it possible to more effectively prevent areverse direction insertion of the rechargeable battery 2 and to moreeffectively prevent an external short circuit between the flange part631 of the terminal plate 63 and the case 20.

In the direction determining member 70, a diameter direction length D2of the plane portion 71 may be equal to or less than a length H2 in theheight direction of the side portion 72 (D2 H2). Therefore, although thediameter direction length D2 may be short, the length H2 in the heightdirection makes it possible to secure a sufficient fastening force ofthe direction determining member 70 to the case 20.

In an embodiment, an insulating member 62 disposed on an exteriorcircumference of the tab connection portion 632 is installed on theinner surface of the cap plate 31. The insulating member 62 may form anelectrically insulating structure between the cap plate 31 and thesecond electrode tab 52, and between the cap plate 31 and the electrodeassembly 10.

The insulating member 62 includes a through hole 621 corresponding tothe terminal hole 311 of the cap plate 31. The through hole 621 allowsthe second electrode tab 52 to be connected to the inner surface of thetab connection portion 632. In an embodiment, the through hole 621 has asmaller diameter than that of the terminal hole 311 to prevent orsubstantially prevent the second electrode tab 52 from being in contactwith the cap plate 31.

While the present invention has been described in connection with whatare presently considered to be some practical example embodiments, it isto be understood that the invention is not limited to the disclosedembodiments. On the contrary, it is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

What is claimed is:
 1. A button cell comprising: a case accommodating anelectrode assembly and having an opening; a cap assembly comprising acap plate coupled to the case to cover and seal the opening, and aterminal plate coupled to the cap plate; and a direction determiningmember covering the cap plate and coupled to the case to define anextended part, wherein the direction determining member comprises: aplane portion covering a portion of the cap plate; and a side portionextending from the plane portion along a side of the case so as to coverand be adjacent and directly coupled to a part of the side of the case.2. The button cell of claim 1, wherein the electrode assembly comprisesa first electrode, a second electrode, and a separator therebetween, thecase is connected to the first electrode via a first electrode tab, andthe terminal plate is connected to the second electrode via a secondelectrode tab.
 3. The button cell of claim 2, wherein the cap plate iselectrically connected to the case, and the cap plate and the terminalplate are thermally fused with a thermal fusion member therebetween andare electrically insulated from each other.
 4. The button cell of claim2, wherein the terminal plate comprises: a flange part between the capplate and the electrode assembly and electrically insulated from andattached to an inner surface of the cap plate; and a protruded terminalprotruded outside from the flange part to be inserted into a terminalhole of the cap plate and electrically connected to the second electrodetab via an inner surface of the terminal plate.
 5. The button cell ofclaim 4, wherein an outer surface of the protruded terminal and an outersurface of the cap plate define a plane surface and are separated fromeach other at a same height based on a bottom of the case.
 6. The buttoncell of claim 5, wherein the plane portion comprises a through holecorresponding to the protruded terminal so as to cover the outer surfaceof the cap plate while exposing the protruded terminal, and the sideportion extends along the side of the case from an outer surface of theplane portion.
 7. The button cell of claim 6, wherein the directiondetermining member comprises an electrically insulating material toelectrically insulate between the outer surface of the protrudedterminal and the outer surface of the cap plate.
 8. The button cell ofclaim 7, wherein the through hole of the direction determining member isconcentric with the terminal hole of the cap plate, and a diameter ofthe through hole is smaller than a diameter of the terminal hole,thereby covering an entire outer surface of the cap plate at a side ofthe protruded terminal.
 9. The button cell of claim 7, wherein thedirection determining member comprises polypropylene, polyethylene,polyethylene terephthalate, polyethylene naphthalate, resin, or rubber.10. The button cell of claim 6, wherein a diameter direction length ofthe plane portion is equal to or greater than a length in a heightdirection of the side portion.
 11. The button cell of claim 2, whereinthe terminal plate comprises: a flange part outside the cap plate andelectrically insulated from and attached to an outer surface of the capplate; and a tab connection portion protruded inside from the flangepart to be inserted into a terminal hole of the cap plate andelectrically connected to the second electrode tab via an inner surfaceof the terminal plate.
 12. The button cell of claim 11, wherein, basedon a bottom of the case, the outer surface of the cap plate is coveredby the flange part, and a remaining exposed surface of the cap platedefines a plane surface.
 13. The button cell of claim 12, wherein theplane portion comprises a through hole corresponding to the flange partso as to cover the exposed surface of the cap plate while exposing theflange part, and the side portion extends along the side of the caseoutside the plane portion.
 14. A button cell comprising: a caseaccommodating an electrode assembly and having an opening; a capassembly comprising a cap plate coupled to the case to cover theopening, and a terminal plate coupled to the cap plate; and a directiondetermining member covering the cap plate and coupled to the case todefine an extended part, wherein the electrode assembly comprises afirst electrode, a second electrode, and a separator therebetween, thecase is connected to the first electrode via a first electrode tab, andthe terminal plate is connected to the second electrode via a secondelectrode tab, wherein the terminal plate comprises: a flange partoutside the cap plate and electrically insulated from and attached to anouter surface of the cap plate; and a tab connection portion protrudedinside from the flange part to be inserted into a terminal hole of thecap plate and electrically connected to the second electrode tab via aninner surface of the terminal plate, wherein, based on a bottom of thecase, the outer surface of the cap plate is covered by the flange part,and a remaining exposed surface of the cap plate defines a planesurface, wherein the direction determining member comprises: a planeportion comprising a through hole corresponding to the flange part so asto cover the exposed surface of the cap plate while exposing the flangepart; and a side portion extending along a side of the case outside theplane portion so as to cover and be coupled to a part of the side of thecase, and wherein, based on the bottom of the case, a height of theplane portion is equal to or less than a height of the flange part. 15.The button cell of claim 13, wherein a diameter direction length of theplane portion is equal to or less than a length in a height direction ofthe side portion.
 16. The button cell of claim 13, further comprising aninsulating member on an exterior circumference of the tab connectionportion and arranged at an inner surface of the cap plate.
 17. Thebutton cell of claim 1, wherein the direction determining member definesa step on a side of the case by the extended part.
 18. The button cellof claim 1, wherein the case defines a first diameter at an outersurface in a diameter direction at a lower portion, and the directiondetermining member is coupled to an upper portion of the case to definea second diameter that is larger than the first diameter in the diameterdirection.